Self guided lawn mowers, as well as navigation systems in which a vehicle follow a guide path are known in the art. U.S. Pat. No. 4,679,152, issued to Perdue discloses a navigation system and method for guiding a mobile robot employing a plurality of sensors that relates to guiding a vehicle to a charging station. Such a guiding system is used to allow a mobile robot to detect and mate with a floating charging unit and does not relate to the guidance of a unit about a predetermined path in order to cover an entire area.
U.S. Pat. No. 4,137,984 issued to Jennings et al. and U.S. Pat. No. 4,730,690 issued to McNutt et al., each disclose bumper mechanisms to prevent forceful collisions with obstacles but which are not intended or optimized for lawn mowers. These devices sense the presence of objects and guide the vehicle around such objects. Again, however, such devices do not relate to the guidance of a unit about a predetermined path in order to cover an entire area.
Numerous patents exists describing navigation systems where vehicles and transporters follow a wire or guide path. For instance, U.S. Pat. No. 4,800,978 issued to Wasa discloses a strip of magnetic material which is detected by detection circuits. Similarly, U.S. Pat. No. 4,742,283 issued to Bolger, U.S. Pat. No. 3,482,644 issued to Krieger et al., U.S. Pat. No. 3,563,327 issued to Mier, and U.S. Pat. No. 3,734,229 issued to Comer describe additional guidance systems. Each of these systems, however, require either a permanent magnet or an electricity conducting electromagnet as a guide path, and they do not discuss a system for following a passive guide path.
U.S. Pat. Nos. 3,800,902 to Keller, 3,550,714 to Bellinger, and 3,095,939 to Hine each disclose automated lawn mowers which use a variety of navigation systems. However, these systems do not include following a buried underground metallic path or a navigation system which includes a marker identification system. U.S. Pat. No. 4,694,639 issued to Chen et al. discloses a robotic lawn mower wherein the path or route is stored in a memory device but does not consider or disclose a system capable of accurately recalibrating the vehicles position to actual landmarks along its path of travel.
Clearly, there is a need for a navigation system for guiding an automatic lawn mower which is capable of recalibrating the units position along a guide path and correct the misalignment of the unit.